Lubricants have a number of functions in tablet manufacture. They prevent adhesion of the tablet material to the surface of dies and punches, reduce interparticulate friction, facilitate the ejection of tablets from the die cavities, and may improve the rate of flow of the tabletable formulation. Commonly used lubricants include talc, magnesium stearate, calcium stearate, stearic acid, and hydrogenated vegetable oils. Most lubricants are used in concentrations from 0.25% to 5.0%, dependent upon the lubricant and tablet granulation. Lubricants are in most cases hydrophobic materials. Poor selection or excessive amounts can result in waterproofing the tablets, resulting in poor tablet disintegration and dissolution of the active ingredient.
The addition of a proper lubricant is highly desirable if the material to be tableted tends to stick to punches and dies. Immediately after compression, most tablets have the tendency to expand and will bind and stick to the side of the die. The choice of the proper lubricant will effectively overcome this. Since they are only required to act at the tooling/material interface, lubricants are generally incorporated at the end of any precompression stage and overmixing avoided, so that the maximum amount is retained on the surface of the particles. Lubricants act by interposing an intermediate layer between the tablet constituents and the die wall, which yields preferentially when the tablet surface moves relative to the die on compression and on ejection.
A problem in the preparation of a water-soluble tablet is the selection of a satisfactory lubricant. Soluble lubricants reported to be effective include sodium benzoate and sodium acetate, sodium chloride, leucine, and high molecular weigh poly(ethylene glycol). However, it has been suggested that formulations used to prepare water-soluble tablets may represent a number of compromises between compression efficiency and water solubility. While magnesium stearate is one of the most widely used lubricants, its hydrophobic properties can retard disintegration and dissolution.
The present invention utilizes a lubricant having the lubricating properties of magnesium stearate without its disadvantages. This lubricant composition is superior to magnesium stearate in promoting proper flow of tablet formulations from the hopper, maintaining an acceptable tablet hardness at various concentrations, maintaining tablet hardness at low compression force settings, and good disintegration and dissolution characteristics.
U.S. Pat. No. 4,310,557 relates to the lubricant formulation used in the present invention as a food emulsifier.